A widely prevailing system, along with the development of higher-capacity recording media in recent years, is one to digitize content data of copyrighted works, such as movies, and distribute the digitalized data stored in digital optical disks or other recording media. With the use of such a system, copyright protection of the content data is necessary, and playback and duplication of the content data must be conducted only within the limits to which the copyright holders have consented. A common system used for protecting copyrighted works from being illegally copied without consent of the copyright holders has a mechanism in which content data is encrypted using a content key that is managed by the copyright holder and then stored in a disk, and only terminals having a corresponding content key can decrypt the encrypted content data in the disk. Here, in order to obtain the content key, an agreement with the copyright holder on provisions regarding copyright protection must be made.
This kind of system has means for informing the user of a playback anomaly in the case when a playback anomaly caused by some reasons during playback is determined on a terminal apparatus that plays back content data read from a recording medium, as disclosed in Patent Reference 1.    <Patent Reference 1> Japanese Laid-Open Patent Application H08-186795